What physical quantity is the same for X-rays of wavelength $10^{-10} m$, red light of wavelength 680 nm and radiowaves of wavelength 50 m?

Speed in vaccum

The correct answer is Option (3) → Speed in vacuum

According to einstein's theory speed of light in vacuum is a universal constant. The physical quantity speed is same for X-ray, red light and radio waves in vacuum and is c = 3 × 10⁸ ms^-1.